PROJECT SUMMARY/ABSTRACT The gastric mucosa of the stomach is continually exposed to a variety of stress factors which can cause local epithelial damage, and potentially lead to larger mucosal lesions, known as peptic ulcers. Peptic ulcer disease (PUD) remains an important issue in healthcare as it occurs in 10-15% of the population and is common in the elderly. New research suggests that proton pump inhibitors (PPIs), the most widely used treatment regimens for PUD, may increase the risk of dementia and chronic kidney disease. As PUD is prevalent in the elderly, the increased risk of dementia with the use of PPIs is alarming. These latest findings highlight the need for a better understanding of the mechanisms of gastric repair that may lead to new therapeutic treatments and help to minimize ulcer incidence or accelerate the repair process. Gastric restitution is the initial event during repair in which damaged cells are expelled away from the site of injury and neighboring viable cells act to cover the denuded mucosa without proliferation. One important factor that has been shown to affect gastric epithelial restitution is the mucus secreted peptide, trefoil factor 2 (TFF2). Work from our lab has shown that TFF2 is necessary for restitution in vivo and requires the sodium hydrogen exchanger isoform 2 (NHE2) for proper repair following damage. Outside of the gastrointestinal tract, evidence points to the potential of TFF2 acting through the TFF receptor CXCR4 which transactivates EGFR. EGFR is known to activate the Erk signaling pathway which has been implicated in NHE2 activation and restitution. Additionally, intracellular calcium (Ca2+) has been shown to be a necessary component within repair. While TFF is known to stimulate protein kinase C (PKC) and Ca2+ mobilization and Ca2+ is known to modulate repair, there is no direct evidence that Ca2+ mobilization is required for TFF2 mediated repair. Due to the complexities of in vivo work and the inconsistences of in vitro immortalized cell lines, the signaling cascade behind TFF2-mediated restitution has yet to be confirmed. Preliminary data have shown that damaged gastric organoids exhibit TFF2-dependent repair, showing key parallels to in vivo findings. This proposal seeks to utilize the novel in vitro gastric organoid system, which has been previously shown to recapitulate native tissue, in order to elucidate the mechanism behind TFF2-driven repair. Based upon preliminary data and previous studies, I hypothesize that TFF2 is the initiating factor which stimulates downstream signaling cascades to promote restitution following repair. To test this hypothesis, I will pursue two specific aims: (1) to determine the role of TFF2/CXCR4 driven EGFR signaling on NHE2 activation and gastric restitution; and (2) to identify the role of PKC signaling and intracellular Ca2+ in TFF2-driven repair. By examining EGFR- and Ca2+-mediated restitution, we have the potential to draw together two separate fields and bring together a number of findings that have previously existed in isolation. The data and experiments presented herein are the logical starting place to address ulcer healing for conditions such as PUD and may provide new therapeutic clinically relevant approaches.